Examination of band bending at buckminsterfullerene (C60)/metal interfaces by the Kelvin probe method
Examination of band bending at buckminsterfullerene (C60)/metal interfaces by the Kelvin probe method
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DOI：
10.1063/1.1504495
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发表时间：
2002-10-01
影响因子：
3.2
通讯作者：
Seki, K
中科院分区：
文献类型：
--
作者：
Hayashi, N;Ishii, H;Seki, K
这项研究解决了在C-60/金属界面的带弯曲的问题。用Kelvin探针法研究了C-60在不同金属基底（Au、Cu和Ag）上沉积时真空能级能量随C-60厚度d的变化。我们观察到：（1）真空能级相对于金属衬底费米能级的能量在小于或等于1 nm处突然移动，在所有被检查的界面处都达到约4.65eV的均匀值;（2）随着C-60的进一步沉积，移动较慢，在与另一个共同值500 nm相似的d处停止。这些突变和渐变分别归因于界面偶极层的形成和费米能级取向导致的能带弯曲。厚层区域的ε（vac）（F）值归因于所研究的特定样品的体积功函数，并且注意到文献中报道的几个单层的值实际上不应被视为体积功函数。这些结果清楚地表明，有必要详细测量高达大厚度有机膜的epsilon（vac）（F），并使用各种金属基底来确定体功函数。在大厚度处，Δ（vac）（F）收敛到一个公共值，表明存在残余杂质。估计其浓度，并检查升华纯化的效果。我们注意到，在这种测量中作为收敛值获得的体积功函数是特定样品的特征，并且可能仍然不对应于真正本征材料的值。(C)2002年美国物理学会。
This study addresses the question of band bending at the C-60/metal interface. The change in the energy of the vacuum level upon the deposition of C-60 on various metal substrates (Au, Cu, and Ag) was examined by the Kelvin probe method under ultrahigh vacuum as a function of C-60 thickness d. We observed (1) an abrupt shift of the energy of the vacuum level relative to the Fermi level of the metal substrate epsilon(vac)(F) at dless than or equal to1 nm, to a uniform value of about 4.65 eV at all of the interfaces examined and (2) a slower shift with further deposition of C-60, which stopped at dsimilar to500 nm at another common value. These abrupt and gradual shifts can be ascribed to the formation of an interfacial dipole layer and to band bending leading to Fermi level alignment, respectively. The value of epsilon(vac)(F) for the thick region is ascribed to the bulk work function of the specific specimen studied, and it is noted that the values reported for a few monolayers in the literature should not actually be regarded as the bulk work function. These results clearly demonstrate the necessity of detailed measurements of epsilon(vac)(F) up to a large thickness of the organic film and of using various metal substrates to determine the bulk work function. The convergence of epsilon(vac)(F) to a common value at a large thickness indicates the existence of remaining impurity. Its concentration was estimated and the effect of purification by sublimation was examined. We note that the bulk work functions obtained as the convergent values in such measurements are characteristic of specific specimens and may still not correspond to the value of the really intrinsic material. (C) 2002 American Institute of Physics.